The term, “phase-change fluid” generally refers to a fluid of which the mechanical and physical properties are changed by external force applied, for example, a shear thickening fluid (STF) and a shear thinning fluid.
The shear thickening fluid (STF) is composed of concentrated suspension colloid prepared by dispersing non-condensed solid particles in a fluid such that, at or beyond a critical shear rate, viscosity thereof may be substantially increased as described previously in Xianzhou Zhang, Weihua Li, Gong, X. L., smart mater. Struct., Vol. 17, 015051 (2008).
Moreover, at a high rate of shear, the viscosity of the shear thickening fluid (STF) may be increased to be solid-like suspension. When shock stress is removed, the shear thickening fluid (STF) may rapidly and reversibly return to be liquid-like state as described previously in Chang, L., Friedrich, K., Schlarb, A. K., Tanner, R., Ye, L., J Mater Sci, Vol. 46, 339-346 (2011).
Meanwhile, the viscosity of the shear thinning fluid may be reduced for ordinary flow with an increase in a rate of shear, and thus, the rate of shear of the shear thinning fluid may be inversely proportional to the viscosity.
Particularly, the phase-change fluid may be liquefied or be liquid-like due to a sharp decrease in the viscosity of nano particles at a high rate of shear. For example, the phase-change fluid may be dispersed in a solvent such as ethylene glycol (EG), propylene glycol (PG), ethylene glycol (EG)/water, or propylene glycol (PG)/water.
In the related arts, nano particles have been substantially studied due to its hydrocluster property between particles. However, the hydrocluster property or phenomenon between nano particles may have a substantial difference as compared with various models that are theologically proposed according to the size of particle. In addition, the phase-change fluid may have a change in viscosity and yield stress when external force is applied. Particularly, when such changes occur rapidly and reversible to the load of external force, it is referred to as a “phase-change effect”. The phase-change fluid may be a Bingham fluid having yield stress, which is obtained as a function of the rate of shear.
The fluid having the phase-change effect may be applied for controllable variable attenuators, such as, brakes, engine mounts, dampers, and bushes, or the power plant, such as, brakes and clutches, and the field where the fluid may be applied has been expanded into a robot industry as well as a vehicle industry and an aircraft industry.
For example, fluid filled hydro bushes are conventional curing rubber parts, prepared by filling a fluid and then sealing, and thus, may provide improved riding quality due to the implement of spring-like characteristic by the combination of rubber elasticity and the fluid.
However, these fluid filled hydro bushes may have technical difficulties. For example, a certain amount of fluid to be injected may not work sufficiently for variously changing vehicle driving states. In addition, when a conventional Newtonian fluid having no change in viscosity according to frequency or a rate of shear is used, the fluid moves along a fluid pathway and absorbs vibration and the hydro bushes that are filled with such fluid have been improved in riding quality. However, high-speed handling performance and durability may deteriorate.
Meanwhile, in the related arts, a fluid filled hydro bush that can control an amount of fluid to be injected has been developed. However, the fluid filled hydro bush may not have a simple constitution and thus manufacturing cost may increase and application to the vehicles may be limited.
In addition, generally used hydro bushes may be advantageous in loss coefficient in a low frequency band, in comparison to solid type bushes. However, their dynamic spring constants may increase substantially with an increase in frequency. Further, from the result of a vehicle driving test, those hydro bushes may have an effect of vibration isolation in a low frequency band, as compared with solid type bushes, but they may vibrate vertically excessively with an increase in frequency. Accordingly, the advantages of both of the hydro bushes and the solid type bushes may be required.
As such, a need for developing intelligent macromolecular dispersed fluid has been increased. For example, by developing a fluid that is filled in hydro bushes, the advantages of a hydro bush in a low frequency band and the advantages of a solid type bush in a high frequency band may be combined and reversible change of phase in accordance with vibration of a vehicle may be obtained.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.